Als is not denying Mathers' whiteness, just saying that it's trumped by class, by economics, by his awareness of being on the outside looking in. It's a terrific point, and Als pushes it further by suggesting that “rap's dissonant sound … was as familiar and natural to the burgeoning artist as the short story form was to Flannery O'Connor.” Notice what he does there: arguing not that rap and short fiction are the same (this would devalue both forms by forcing a false equivalency) but that for these artists, the drive to create comes out of a common otherness.
The O'Connor reference highlights another kind of doubling, since Als has already written about her in the book. What he's getting at is how these artists come together in his imagination, echoing one another and himself. This makes “White Girls” more than a collection of disparate pieces but rather a coherent portrait of Als' inner life.
The focus is privilege, who has it and who will never have it, and what those without it are supposed to do. As Als notes of Capote, “It is hard to garner privilege when you begin with none — for those who have to reach for it, it remains perpetually out of reach.”
more here.